To be CLEAR, this is not the same issue I've seen reported before (at least when I searched) so don't dismiss it as another "Bundles inside of bundles" bug.

You can use bundles to stack empty bundles. 

To Reproduce this issue:

1. Have a chest full of junk items (dosn't matter what) and several empty bundle bags in your inventory
2. Be in survival mode
3. Place any number (up to 16) of your bundle bags into a bundle
4. Fill the rest of your inventory and hot bar with junk items such that there are no empty slots
5. Right click to open the bundle holding the other bundles which will now be disgorged on the ground due to a lack of space
6. You can now pick up the dropped bundles as a stack of empty bundle

See Attached image with a stack of 7 empty bundles in inventory